thermal decomposition of different types of asbestos · thermal decomposition of different types of...

Thermal decomposition of different types of asbestos

R. Kusiorowski • T. Zaremba • J. Piotrowski •

J. Adamek

Bretsznajder Special Chapter

� The Author(s) 2012. This article is published with open access at Springerlink.com

Abstract Given the known carcinogenic effects, asbestos

minerals are considered as general health hazard. There-

fore, the elimination of asbestos materials from the envi-

ronment is necessary. Asbestos minerals should be entirely

transformed to a non-hazardous material. One of these

methods is destructing the fibers structure of asbestos

minerals by thermal treatment. Asbestos minerals are nat-

urally occurring hydrous silicates, so that they decompose

to release water by heating at high temperatures which may

lead to changes in crystal structure and the formation of

new phases without the dangerous properties. In this arti-

cle, thermal behavior of asbestos minerals is investigated to

observe the disappearance of this hazardous structure and

to characterize products obtained by this way. Ten samples

of asbestos minerals (six chrysotile samples from different

locations, two samples of crocidolite, one amosite, and one

tremolite) from different locations were tested. Mineral-

ogical and morphological data (X-ray diffraction, Fourier

transform infrared spectroscopy, and scanning electron

microscopy) were obtained before and after differential

thermal analysis.

Keywords Asbestos minerals � DTA � FT-IR � SEM �Thermal decomposition � XRD

Introduction

Asbestos is a general name applied to a group of silicate

minerals which naturally occur in fibrous form. There are

six principal asbestos minerals (Fig. 1) which are divided

into two main mineral groups: serpentine and amphibole

asbestos. The group of serpentine includes only one fibrous

silicate mineral—chrysotile. This mineral has a layered

silicate structure. The other five asbestos forms belong to

the amphibole type, having chain structure. Minerals such

as actinolite, tremolite, crocidolite (fibrous form of rie-

beckite), anthophyllite, and amosite (fibrous form of

grunerite) are found in this group [1–4].

The mineralogical composition, structure, and physical

properties determined the use of these minerals in industry.

In the past, asbestos was used in about 3,000 different

commercial products [5]. Each type of asbestos has dif-

ferent physical characteristics. Generally, asbestos fibers

are characterized by flexibility, high-tensile strength, large

surface area, incombustibility, abrasion resistance, and

resistance to acids and bases [6–8]. Chrysotile fibers are

extremely thin and are flexible and soft, which can provide

weaving. In turn, amphibole asbestos fibers are harsher and

more brittle than chrysotile [8]. Chrysotile (white asbes-

tos), crocidolite (blue asbestos), and amosite (brown

asbestos) have the largest industrial applications because

these three minerals have desirable properties (Table 1).

In Poland, since the 80s of last century production of

asbestos-containing materials decreased significantly. It

has been proved that asbestos fibers have carcinogenic

effects [9–11]. The most dangerous are respirable fibers,

which can penetrate deeply into the respiratory system,

from where they are not easily removable by the simple

natural cleansing mechanisms. These fibers have a length

greater than 5 lm, a diameter of less than 3 lm, and a

R. Kusiorowski (&) � T. Zaremba � J. Piotrowski

Department of Chemistry, Inorganic Technology and Fuels,

Silesian University of Technology, B. Krzywoustego Str. 6,

44-100 Gliwice, Poland

e-mail: [email protected]

J. Adamek

Department of Organic Chemistry, Bioorganic Chemistry

and Biotechnology, Silesian University of Technology, B.

Krzywoustego Str. 4, 44-100 Gliwice, Poland

123

J Therm Anal Calorim (2012) 109:693–704

DOI 10.1007/s10973-012-2222-9

length to diameter ratio above 3:1 [7]. Carcinogenic

activity of asbestos was the reason for including these

minerals in a list of hazardous materials.

It is therefore advisable to attempt the detoxification of

asbestos minerals and to find the methods based on recy-

cling. The methods which are able to change the harmful

properties of asbestos minerals through the destruction of

the fibrous structure should be considered. Dissolution in

acids [4, 12–17], hydrothermal treatment [18, 19], mech-

anochemical treatment with high-energy milling process

[20], fiber melting and vitrification with fluxes or the use of

plasma technology [21, 22] are the main among the

described methods in technical literature.

One of these methods is also thermal treatment.

Asbestos minerals are naturally occurring hydrous silicates,

so that they decompose to release water by heating at high

temperatures which may lead to changes in crystal struc-

ture and the formation of new phases without the danger-

ous properties. This method can be realized by the

conventional thermal treatment [6, 23–27] or with the use

of microwave radiation [3, 28].

Similar to the clay minerals [29, 30], thermal decom-

position of asbestos minerals generally takes place

according to three stages [7, 31]. The first is associated

with the loss of adsorbed water. The next step is connected

to the removal of structural OH groups from the structure

of asbestos minerals. The last stage which is responsible for

the crystallization of amorphous materials and the growth

new phases occurs after dehydroxylation.

In the case of chrysotile asbestos [Mg3(OH)4Si2O5],

which was the most abundant and most widely investi-

gated, results reported in several studies [6, 7, 32–36] show

that chrysotile with the loss of chemical combined water

transforms into an anhydrous phase (metachrysotile)

around 500–750 �C (with a maximum rate above 700 �C).

Rapid recrystallization of anhydrous phase occurs after this

stage at above 800 �C. The main product of this transfor-

mation is forsterite (Mg2SiO4). Enstatite (MgSiO3) can be

formed at higher temperature also. These minerals have not

fibrous structure and carcinogenic properties. The above

transformations are represented by the following reaction

path [6]:

Mg3 OHð Þ4Si2O5 ! Mg3Si2O7 þ 2H2O! Mg2SiO4 þMgSiO3

chrysotile metachrysotile forsterite enstatite

In contrast to the chrysotile asbestos, the specialist literature

which describes the thermal decomposition of amphibole

asbestos is much less. The decomposition of crocidolite

{Na2Fe3Fe2[(OH)Si4O11]2} takes place also in three stages:

loss of physically combined water, loss of chemically

combined water, and final breakdown into simpler phases.

Typical DTA curves for crocidolite specimens show an

exothermic peak at 410–420 �C, a sharp endothermic peak

with weight loss at 895–910 �C (dehydroxylation) and a small

exothermic peak at 920–960 �C (crystallization). Sometimes

endothermic effect is observed, which is caused by the

decomposition of carbonate impurities [37]. The exothermic

thermal effect at *400 �C is associated with oxidation. This

redox reaction involves the conversion of Fe2? to Fe3? [31].

According to Fujishige et al. [38] weight loss of crocidolite was

not observed above *700 �C. However, on DTA curve, the

authors observed strong endothermic peak (Tmax * 930 �C)

without weight change. SEM observations of the specimens

obtained by thermal treating show fibers which were melt-

bonded with each other to form a large densified fiber. The

main mineral compound which was formed from crocidolite

after thermal treatment (isothermal firing) may be acmite

Table 1 Physical and chemical properties of selected asbestos fibers [1, 2, 8]

Property Chrysotile Crocidolite Amosite

Color Usually white to grayish green Blue to black Yellowish gray to dark brown

Luster Silky Silky to dull Vitreous to pearly

Hardness (Mohs) 2.5–4.0 4.0 5.5–6.0

Density (g cm-3) 2.4–2.6 3.2–3.3 3.1–3.2

Tensile strength (MPa) 1,100–4,400 1,400–4,600 1,500–2,600

Resistance to acids Weak Good Fair

Resistance to alkalies Very good Good Good

ASBESTOS

Serpentine Amphiboles

Chrysotile (white asbestos) Mg3(OH)4Si2O5

Crocidolite (blue asbestos)

Na2Fe3Fe2[(OH)Si4O11]2

Anthophyllite (Mg,Fe)7[(OH)Si4O11]2

Actinolite Ca2(Mg,Fe)5[(OH)Si4O11]2

Tremolite Ca2Mg5[(OH)Si4O11]2

Amosite (brown asbestos)

(Fe,Mg)7[(OH)Si4O11]2

Fig. 1 Type of asbestos

694 R. Kusiorowski et al.

123

(NaFeSi2O6), ferrosilite (FeSiO3), magnetite (Fe3O4),

hematite (Fe2O3), and cristobalite (SiO2) [31, 38].

The decomposition of amosite {(Fe,Mg)7[(OH)-

Si4O11]2} and tremolite {Ca2Mg5[(OH)Si4O11]2} follows a

very similar pattern to previously described asbestos, but

requiers higher temperature. The final products of amosite

decomposition above 900 �C (at isothermal soaking) are a

spinel, hematite, magnetite, and cristobalite [31, 38]. The

thermal analysis of tremolite mainly shows an endothermic

peak at *950 �C due to the dehydroxylation reaction [6].

Again complete recrystallization to high-temperature pha-

ses was obtained by firing at 1,100 �C for 1 h. In this case,

diopside (CaMgSi2O6), enstatite (MgSiO3), and cristobalite

are obtained.

The aim of the research presented in this study is to

determine and compare the structural and phase transfor-

mations which are subject to different types of asbestos

minerals during dynamic heating to 1,000 �C by DTA

method in order to verify the disappearance of crystalline

asbestos fibers.

Experimental

In the present study, 10 different types of asbestos were

examined (Table 2). Most of the samples came from Czesław

Poborski Museum of Mineral Deposit Geology at the Institute

of Mining and Geology, the Silesian Technical University in

Gliwice. Due to the small amount of obtained specimens, they

were characterized as received. Specimens of chrysotile

asbestos came from Poland, Russia (two samples), Canada,

and Australia. One sample of crocidolite asbestos from

Republic of South Africa, one specimen of amosite from

Russia, and one specimen of tremolite from Italy were

examined also. In addition, chrysotile and crocidolite were

also used in research, which have been separated from cor-

rugated asbestos-cement (a-c) slates. In this case, any

additional purification was not applied. All asbestos samples

were studied by differential thermal analysis (DTA) and

thermogravimetric analysis (TG). Mineralogical composition

and morphology both of natural and heated samples (after

Table 2 Origin and LOI of tested samples

Symbol Type of asbestos Origin LOI (%) (theoretical) LOI (%) (based on TG)

C1 Serpentine Chrysotile Poland 13.0 15.0

C2 Chrysotile Russia 14.2

C3 Chrysotile Russia 17.0

C4 Chrysotile Canada 14.2

C5 Chrysotile Australia 14.5

C6 Chrysotile a-c slate 24.0

T Amphiboles Tremolite Italy 2.2 2.2

K1 Crocidolite Republic of South Africa 1.9 3.2

K2 Crocidolite a-c slate 17.5

A Amosite Russia 2.0 1.2

Ch

Ch

Ch Ch

Ch –chrysotile

C6

Ch

Ch

Ch C5Ch

Ch

Ch

Ch

Ch

Ch C4

C3ChCh

Ch

Ch

Ch C2

C1Ch

Ch

Ch

Ch

2θ/°

Inte

nsity

/a.u

.

10 15 20 25 30 35 40 45 50 55 60 65 70

Fig. 2 XRD patterns of natural chrysotile asbestos samples

Thermal decomposition of different types of asbestos 695

123

DTA, unchanged form after removing from the crucible) were

evaluated by X-ray diffraction (XRD), Fourier transform

infrared spectroscopy (FT-IR) as well as scanning electron

microscopy (SEM). To estimate the grinding ability of the

obtained materials, additional SEM analysis of thermal-trea-

ted samples after manually pulverized in a hand agate mortar

was carried out.

Thermal analysis (DTA and TG) was performed using a

Paulik–Paulik–Erdey (MOM, Hungary) type derivatograph

within the range of temperature 20–1,000 �C. The condi-

tions were: mass of sample 200 mg, air atmosphere, heat-

ing rate 10 K min-1, platinum crucible and Al2O3 as the

reference material. XRD analysis of examined samples was

carried out using a Seifert XRD-3003 TT diffractometer

(Cu Ka radiation, Ni filter, 40 kV, 30 mA). The micro-

structure of samples was examined by SEM (Tesla BS 340,

the Czech Republic). Observations were made after coating

the samples’ surfaces with a thin layer of gold. IR spectra

were measured on a Nicolett 6700 FT-IR spectrophotom-

eter (ATR method).

Results and discussion

Chrysotile asbestos

X-ray diffraction study showed that the main mineral

component of the all tested samples was well-crystallized

chrysotile. This is indicated by the characteristic narrow

and intense two major diffraction peaks at about 12� and

25� (2h) (Fig. 2). X-ray analysis does not show the pres-

ence of any impurities.

The FT-IR spectra of all chrysotile samples are presented in

Fig. 3. In the region 3,000–4,000 cm-1, two IR bands are

well visible. First strong at 3,681–3,686 cm-1 and second

which is weaker at 3,640–3,650 cm-1. The IR band at

C6

C5

C4

C3

C2

C1

4000 3500 3000 2500 2000 1500 1000 500

Wavenumbers/cm–1

Tran

smita

nce

3681

3640

14471070

1010

1070

1020

935

591

951591

10101078

947

601

3683

3640

14211070

1010

1482

36863650

3650

3683

1070

1010942

603

1418

1080606

955603

1030947

36833650

3683

3650

Fig. 3 FT-IR spectra of natural chrysotile asbestos samples

0 200 400 600 800 1000

Temperature/°C

C1

C2

C3

C4

C5

C6

360

350

820

830

700

650

820

720

830

720520400

330

700

820

820

720

680730

DTA

exo

Fig. 4 DTA curves of chrysotile asbestos samples


123

3,681–3,686 cm-1 can be assigned to the surface Mg–OH

stretch vibration, whereas the second band can be linked to the

inner Mg–OH stretch vibration [38]. This confirms the

assignment of the OH doublet to the external and internal

Mg–OH groups in chrysotile asbestos [33]. The IR bands

recorded in the region *1,080–935 cm-1 are typical of the

Si–O–Si stretches in the silica network. The first (at

*1,070–1,080 cm-1) can be assigned to the out-of-plane

symmetric stretching vibration of the silica sheet. Other two

bands (at *1,010–1,030 cm-1 and *935–955 cm-1) come

from the in-plane Si–O stretching. The IR band at

591–606 cm-1 can be assigned to the inner Mg–OH vibration

[39]. For several samples, FT-IR analysis showed the presence

of some impurities. The IR bands recorded in the region

*1,400–1,500 cm-1 may indicate the presence of carbonates.

Table 2 shows theoretical (based on chemical formula)

and calculated (based on TG measurement) values of loss

of ignition (LOI). Higher LOI for each chrysotile asbestos

sample may also indicate the presence of some impurities.

The highest LOI value was obtained for C6 sample (from

a-c slate). This is related with the presence of calcite and

other cementitious phases, which could not be thoroughly

removed from the asbestos fibers.

The thermal behavior of the chrysotile asbestos samples

is represented in Fig. 4. In the temperature range

600–800 �C, chrysotile Mg3(OH)4Si2O5—regardless of

origin and deposit—losses the chemical bonded water

(Fig. 4, strong endothermic peak with Tmax 700–730 �C).

This causes complete breakdown of the mineral structure

and formation of an amorphous material, metachrysotile. In

the next stage, it occurs the crystallization of this amor-

phous structure and the creation of forsterite Mg2SiO4

(Fig. 4, exothermic peak at *820–830 �C). Forsterite

belongs to the orthosilicates and do not exhibits the car-

cinogenic properties [40]. For some samples, DTA analysis

clearly showed the presence of impurities. The exothermic

peaks at 330–360 �C may be related with the combustion

of organic matter [3]. A weak endothermic peaks at *400

10 15 20 25 30 35 40

2θ/°

45 50 55 60 65 70

Inte

nsity

/a.u

.

F – forsterite

F F FF

F

F

F FF

FF

F

FF

F

FFFF

FF F F

FF F

FF

F

FF

FF

F FF

FC1

C2

C3

C4

C5

C6

Fig. 5 XRD patterns of chrysotile asbestos samples after thermal

treatment

4000 3500 3000 2500 2000 1500 1000 500

Wavenumbers/cm–1

Tran

smita

nce

870

841

611984

1070

872

839

984

1070

613

874

985839

612

873

842

984

1080

610

872

837

6129841070

872

837

611984

14173672

C5

C6

C4

C3

C2

C1

Fig. 6 FT-IR spectra of chrysotile asbestos samples after thermal

treatment


123

and at *520 �C for C3 sample may indicate the presence

of brucite [Mg(OH)2] [24] and portlandite [Ca(OH)2] [41],

respectively. In the case of C6 sample (chrysotile from a-c

slate), the cementitious matrix from the asbestos fibers

could not be completely removed. The characteristic peak

of dehydroxylation of chrysotile asbestos is masked by the

endothermic reaction related with the thermal decomposi-

tion of calcite (CaCO3) which came from carbonatization

of cement [41]. The presence of inflection point on DTA

curves at 650–680 �C (samples C1 and C5) may indicate

the presence of magnesite (MgCO3) [42].

The obtained results for the thermal decomposition of

chrysotile asbestos were confirmed by the XRD analysis.

The typical narrow and intense two major diffraction peaks

of chrysotile (Fig. 2) are disappeared, whereas on the XRD

pattern of chrysotile asbestos after thermal analysis (Fig. 5)

can be seen new peaks (the strongest at 35�–40� 2h). They

indicate a formation of forsterite. Their weak intensity is

due to the measurement conditions, because the study was

performed on the material after DTA analysis without the

isothermal soaking.

The increased background in the range 10�–15� 2h may

indicate the presence of metachrysotile with X-ray amor-

phous structure. In accordance with Langer [43], the

complete dehydroxylation of chrysotile leads to the

breakdown of the mineral structure and creation of anhy-

drous phase, i.e., material which does not show the prop-

erties of chrysotile. Cattaneo et al. [24] stated that the

Fig. 7 SEM image of C5 sample (chrysotile from Australia).

a Natural, b directly after thermal treatment, and c after thermal

treatment and soft crush in mortar

Fig. 8 SEM image of C6 sample (chrysotile from a-c slate).

a Natural, b directly after thermal treatment, and c after thermal

treatment and soft crush in mortar


123

amorphous dehydroxylate of chrysotile is extremely

unstable (e.g., in comparison with metakaolinite) and for-

sterite is the first observed reaction product.

Thermal behavior of tested sample of chrysotile was

also confirmed by infrared analysis (Fig. 6). The charac-

teristic double band at 3,640–3,680 cm-1 corresponding to

OH stretching vibrations of chrysotile is disappeared. Only

for sample C6 (from a-c slate), one can observe a weak

signal in this region. It may be the result of the presence of

Ca(OH)2. It was created from the highly hygroscopic CaO

after thermal decomposition of calcite. Heating the samples

causes appreciable others changes in their FT-IR spectra,

which confirms a conclusion about the structural transfor-

mations in heating. The characteristic triplet within

935–1,080 cm-1 (Fig. 3) is clearly shifted toward lower

frequencies (Fig. 6). The IR bands recorded in the region

*985–837 cm-1 and at *610 cm-1 are typical for the

forsterite crystal [33, 44, 45].

The SEM images of selected natural asbestos, materials

obtained after DTA analysis, without grinding treatment

and after soft crush in hand agate mortar are presented on

Figs. 7 and 8. For the natural chrysotile samples, the SEM

images show the typical bundles of asbestos, which occur

as a combination of large amount of very thin fibers. They

are intertwined with each other. In contrast to amphibole

asbestos (Figs. 14, 15, 16), chrysotile fibers are more

flexible. Also, fine grains from cement matrix can be seen

on the fibers of sample from a-c slate (Fig. 8).

After thermal treatment, the fibrous morphology of

obtained samples is maintained, but this material has very

fragile fibers. By mechanical interference, this material was

easily disintegrated into powder. Even after the soft and

hand crush in agate mortar powder material was obtained,

where fibrous morphology is not retained. This is in

accordance with the results presented in [25, 36].

Amphibole asbestos

In the case of amphibole specimens, XRD study also

confirmed that the main mineral in tested samples was

2θ/°

10 15 20 25 30 35 40 45 50 55 60 65 70

Inte

nsity

/a.u

.

TTTTT

TT

T

T

KKK

KK

K

K

K

K

K KK

KK

A

AAA

A

A – amosite

T – tremoliteK – crocidolite

A

K2

K1

T

T

Fig. 9 XRD patterns of natural amphibole asbestos samples

4000 3500 3000 2500 2000 1500 1000 500

Wavenumbers/cm–1

Tran

smita

nce

916

942

984

757

683

6421092

3674

969

880776

6326901103

1143

36193640

36603630

1447972 855

1099

1148778

965

891772

702630

10791128

3638 3618

A

K2

K1

T

Fig. 10 FT-IR spectra of natural amphibole asbestos samples


123

asbestos mineral (Fig. 9). Since the amosite, crocidolite,

and tremolite belong to one group of minerals (amphibole),

the XRD patterns of these minerals are similar.

The FT-IR spectra of all amphibole samples are pre-

sented in Fig. 10. As in the case of chrysotile asbestos, in

the high-wavenumbers region absorbance bands related to

the OH stretch are visible. However, their intensity is

lower. The reason for this is a much lower part of this

group in samples. The IR bands recorded in the region

below *1,100 cm-1 are typical of the Si–O–Si stretches in the

silica network. For the K2 sample (crocidolite from a-c slate),

the IR bands recorded in the region *1,400–1,500 cm-1

indicate the presence of carbonates.

Considering the values of LOI for the amphibole

asbestos (Table 2), it can be noted that for the tremolite and

crocidolite samples, this value is equal or higher in com-

parison to theoretical. Similar to chrysotile asbestos

(sample C6), for the sample K2 (crocidolite from a-c

slate), the LOI is much greater. This is related also with the

presence of calcite and other cementitious phases, which

0 200 400 600 800 1000

Temperature/°C

DTA

exo

TT

K1

K2

A

340

940

800

940

Fig. 11 DTA curves of amphibole asbestos samples

800 900 1000

96

96.5

97

97.5

98

98.5

99

99.5

100m[%]K1

DTA

exo

Temperature/°C

DTG

DTA

TG

Fig. 12 DTA, TG, and DTG curves of exemplary crocidolite

asbestos sample in selected temperature range

4000 3500 3000 2500 2000 1500 1000 500

Wavenumbers/cm–1

Tran

smita

nce

920947 869

1069

639758

908992

1080789

876

848

995

1066

923801

1190

14403650

K2

A

K1

T

Fig. 13 FT-IR spectra of amphibole asbestos samples after thermal

treatment


123

could not be completely removed from the asbestos fibers.

Only for the amosite sample, the LOI was lower than the

calculated theoretical value. This indicates directly to the

only initiated process of thermal degradation of this

asbestos sample during non-isothermal heating to a

1,000 �C.

Based on thermal analysis (Fig. 11), it can be concluded

that dehydroxylation of amphibole asbestos—in compari-

son to chrysotile (Fig. 4) —requires a higher temperature

of thermal treatment. In the case of crocidolite asbestos

samples (K1 and K2) on DTA curves appear endothermic

peaks at *940 �C (Fig. 11). It may be caused by the loss

of chemical bonded water [37] or in accordance with

Fujishige et al. [38] by partially melted fibers. The second

way was confirmed by TG analysis (Fig. 12) and following

SEM observation of the samples after thermal analysis

(Fig. 15b). In the case of TG analysis, this endothermic

peak was without weight change. According to literature

[31, 38], one of the minerals which are formed during

thermal decomposition of crocidolite is acmite (NaFe-

Si2O6). This mineral (pure) has the incongruent melting

point with separation of hematite at 990 ± 5 �C [46]. As a

result of its creation in the case of thermal decomposition

of crocidolite asbestos, it could take place partially melting

fibers. However, this statement requires further study.

For the K2 sample (crocidolite from a-c slate) can be

seen also endothermic peak with Tmax = 800 �C which

corresponds to the decomposition of calcite from cemen-

titious matrix. Thermal decomposition of tremolite asbes-

tos (sample T) was initiated only. At 950 �C can be seen

(Fig. 11) the beginning of endothermic peak of dehydr-

oxylation process. For the amosite asbestos—in the

2θ/°

10 15 20 25 30 35 40 45 50 55 60 65 70

Inte

nsity

/a.u

.

T

K1

K2

A

H

Cr

HH

H H

W

W

W – wollastoniteH – hematiteCr – crystobalite

Fig. 14 XRD patterns of amphibole asbestos samples after thermal

treatment

Fig. 15 SEM image of K1 sample (crocidolite). a Natural, b directly

after thermal treatment, and c after thermal treatment and soft crush in

mortar


123

investigated temperature range and for linear heating—

there was no typical peak for dehydroxylation. Although, it

can be concluded that this decomposition has already been

initiated (absence of a band in the high-range wave num-

bers at 3,640–3,680 cm-1 which correspond to the OH

stretching (Fig. 13). Thermal decomposition of other

amphiboles asbestos also confirmed IR spectra (Fig. 13),

where beyond the absence of OH bands can be seen clearly

shifts to lower frequencies of the Si–O–Si bands. The

temperature range of non-isothermal heating was too low,

so cannot create well-crystallized products of the thermal

decomposition of amphiboles asbestos. On the XRD

patterns (Fig. 14), one can observe poor traces of new-

formed crystal phases. In the case of amosite asbestos

created X-ray amorphous material.

Amphibole asbestos minerals after thermal treatment

which was used in this study also show high-grinding

ability. SEM images of natural asbestos, material obtained

after DTA analysis, without grinding treatment and after

crush in hand mortar are presented on Figs. 15, 16, and 17.

Even for amosite asbestos, where decomposition process

was only initiated, obtained material was brittle and fragile.

Further fragmentation is possible, e.g., by grinding the

material in a vibratory mill [7, 27].

Fig. 16 SEM image of T sample (tremolite). a Natural, b directly

after thermal treatment, and c after thermal treatment and soft crush in

mortar

Fig. 17 SEM image of A sample (amosite). a Natural, b directly after

thermal treatment, and c after thermal treatment and soft crush in

mortar


123

Conclusions

The thermal decomposition of raw natural asbestos min-

erals was characterized by DTA, XRD, FT-IR, and SEM.

Thermal treatment is one of the methods that can recycle

asbestos fibers as it causes the loss of their dangerous

properties. Depending on the type of asbestos, a different

temperature is required (about 700–800 �C for chrysotile

and more than 900 �C for the amphiboles asbestos). As a

result of this process, the mineral structure is changed

through dehydroxylation which leads to the formation of

X-ray amorphous and anhydrous phase with the main-

taining of fibrous morphology. Even it is retained, miner-

alogical and infrared data show that the structure of

asbestos is destroyed. The obtained materials have high-

grinding ability and they are easily milled to pulverulent-

shaped materials which can be used as one of raw materials

for further production, for example, in ceramic industry.

Acknowledgements We gratefully acknowledged two anonymous

reviewers for their careful revision of the manuscript and for helping

in clarify and improve the English language.

Open Access This article is distributed under the terms of the

Creative Commons Attribution License which permits any use, dis-

tribution, and reproduction in any medium, provided the original

author(s) and the source are credited.

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